Why was she looking at me like she hated me?

I was walking through town with my mother when we reached this house that had a bunch of people around my age messing around. A few of them were getting in the car. I turned my head for a second towards the car and this girl from my middle school was basically glaring up at me from the other side of the car. OK, I haven't seen this chick in two or three years and the most of done to her was say she was kind of bitchy in 7th or 8th grade and like her ex-boyfriend at the time in 9th grade. Didn't really even like him, just thought he was attractive because the boy had a nice body. We talked a minimum of twice until we stopped talking the day she broke up with him or whatever. Why the hell is she glaring at me because I've done nothing to her?